Magcard payment is used more and more widely, and POS machines are used more and more. Since a magnetic head of a POS machine needs to read account information of cards, for example, bank cards, credit cards, and the like of users, in order to prevent account information of the users from being stolen, the security protection for the magnetic head of the POS machine is particularly important. When the POS machine swipes a card, a magnetic stripe area of the card needs to pass the magnetic head, such that the magnetic head reads account information in the card; therefore, the magnetic head is usually mounted on a strip-shaped frame, the card is guided through the frame, thus it is ensured that the magnetic head can well read the information in the card, and the magnetic head is connected with a main board of the POS machine through wires. However, when a user uses the POS machine to swipe a card, he/she may not observe carefully, or may not know whether an additional magnetic head has been mounted on the magnetic head frame. As a result, some malicious persons may illegally mount magnetic heads on magnetic head frames to steal user information.